1. Stress Analysis of Universal Tilt Kit Attachment Points
Project: Stress analysis of Universal Tilt Kit attachment points under worse case hurricane loading (500 lbf per attachment point).
Modeling Assumptions and Details: A finite element analysis (FEA) model was constructed based on geometry provided by the Kineo Design group. The attachment point structures for the solar panel were idealized using 8-node brick elements, beam elements for the bolts and rigid links for the bolt attachments. An additional plate model was constructed to investigate the stress and buckling behavior of the rear support leg.
A high-strength aluminum material model was used for all structures with a yield stress of 30,000 psi and an ultimate tensile stress of 36,000 psi at an elongation of 6% at failure. A nonlinear analysis was performed due a slight overload condition. It was assumed that the material yielded at 30,000 psi and would fail at 36,000 psi after a plastic elongation of 6%.
A 500 lbf load was applied via an aluminum extrusion section of the solar panel frame. Symmetry was exploited and half-symmetric section of the structure was analyzed using a total load of 250 lbf. The Eigenvalue buckling analysis was performed on the Rear Extension Leg with the 500 lbf downward load since an uplift load would not cause buckling.
Units used for this analysis are lbf, sec, in. Stress results are presented in psi and deflection in inches.
All modeling work was done with FEMAP V9.3.1 and analyzed using NX Nastran V5.0.mp1
Summary: Stress results for the SunEarth Universal Tilt Kit adaptors (front and rear) indicate that they will support the one-time application of a 500 lbf load in the uplift and downward directions. A minor amount (less than 1%) of plastic yielding is indicated but the Adaptors structural integrity remains intact.
An Eigenvalue buckling analysis of the Rear Adaptor Extension Leg indicates a buckling factor in excess of 5x of the applied load. As such, buckling of the leg is not predicted.

2. FEA Model Background

3. Rear Adaptor
Front Adaptor
Geometry for SunEarth-Kineo Design Universal Tilt Kit. The front and rear adaptors are shown that comprise the “Universal Tilt Kit”.

4. 500 lbf load is evenly distributed over this extrusion segment
500 lbf load is evenly distributed over this extrusion segment. The same load pattern was used for the Rear Adaptor.
View of the Front Adaptor. The Rear Adaptor has a similar configuration. The geometries are half-symmetric. The load is assumed to be aligned with the solar panel extrusion.

5. The structure was held vertically by cylindrical constraints appled along the bottom of the hole:
Loads are shown for the Front Adaptor model. The half-symmetric model uses a distributed load of 250 lbf over the section of the solar panel extrusion. Beam elements are used to model the bolted connections.

6. Local coordinate system for solar panel extrusion.
The constraint set is uses locally defined coordinate systems to enforce specific constraint actions. The solar panel is assumed to be fixed in the Z-direction within its local coordinate system. That is, the solar panel is rigid and does not move along its normal axis (z-direction). At the base of the Adaptor, local coordinate systems defined the constraints for rigid bolts.

7. The Rear Adaptor used the same load and constraint setup.

8. The Rear Adaptor used the same load and constraint setup.

9. The Rear Adaptor support leg was also analyzed for stress and buckling
The Rear Adaptor support leg was also analyzed for stress and buckling. A simple plate model was constructed and analyzed using an Eigenvalue buckling analysis.

10. Stress Results for Front Adaptor under 500 lbf Load: Rev-0
Analysis Notes: Stress results are presented for the 500 lbf uplift and 500 lbf downward load cases.
A nonlinear analysis was performed to allow the adaptor to slightly plastically deform around high stress regions.
Stress results are presented in lbf/in2 and deflections are in inches.
The deformation of the structure has been scaled by10x to better visualize the deflection behavior of the Adaptor under the various wind loads.

11. The maximum von Mises stress is 30,482 psi
The maximum von Mises stress is 30,482 psi. This stress indicates a very minor amount of plastic yielding has occurred within the structure. Considering that the load case is assumed to be a peak, one-time load (hurracaine force event), this amount of plastic yielding is acceptable.

12. Another view of the uplift load case. The deflection is scaled by 10x.

13. Another view of the uplift load case with the extraneous parts removed from the graphics view.

14. This analysis has the load reversed and the solar panel extrusion is pushing down on the Front Adapter with a force of 500 lbf (250 lbf via symmetry). The maximum von Mises stress is 30,351 psi.

15. The maximum von Mises stress is 20,972 psi in the main structural components under the 500 lbf downward load.

16. Stress Results for Rear Adaptor under 500 lbf Load: Rev-0
Analysis Notes: Stress results are presented for the 500 lbf uplift and 500 lbf downward load cases.
A nonlinear analysis was performed to allow the adaptor to slightly plastically deform around high stress regions.
Stress results are presented in lbf/in2 and deflections are in inches.
The deformation of the structure has been scaled by10x to better visualize the deflection behavior of the Adaptor under the various wind loads.

17. The maximum von Mises stress is 30,720 psi under the 500 lbf upward lift load. The deflection has been scaled by 10x.

18. Side view. The deflection has been scaled by 10x.

19. The maximum von Mises stress is 30,723 psi in the main structural components under the 500 lbf upward lift load.

20. The maximum von Mises stress is 30,415 psi under the 500 lbf downward load. The deflection has been scaled by 10x.

21. Side view.

22. The maximum von Mises stress is 30,056 is the main structural component.

23. Stress Results for Rear Adaptor Extension Leg under 500 lbf Load: Rev-0
Analysis Notes: Stress and Eigenvalue buckling results are presented for the 500 lbf downward load case. The 500 lbf uplift load case does not pose a structural challenge for the Extension Leg.
Stress results are presented in lbf/in2 and deflections are in inches.

24. The maximum von Mises stress is 20,836 psi under the 500 lbf downward load.

25. The maximum von Mises stress is 20,836 psi is located in the bolted extrusion section.

26. The maximum von Mises stress is 11,629 psi in the section leg.

27. The Eigenvalue buckling mode is 6. 63x500 lbf
The Eigenvalue buckling mode is 6.63x500 lbf. That is, buckling would occur somewhere about 3,000 lbf.

28. The second Eigenvalue buckling mode is at 7. 48
The second Eigenvalue buckling mode is at It is presented just for completeness.

29. Appendix
Executing Engineer Certification

30. Executing Engineer Certification

31. All work within this report was done by George Laird, Ph.D., P.E.